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| United States Patent |
5,276,157
|
|
Rieker
|
January 4, 1994
|
Process for the purification of 2,3-pyridine and quinolinedicarboxylic
acid diester compounds
Abstract
The present invention provides a process for the purification of
2,3-pyridine and quinolinedicarboxylic acid diester compounds via
extraction with a mineral acid.
| Inventors:
|
Rieker; William F. (Clark, NJ)
|
| Assignee:
|
American Cyanamid Company (Wayne, NJ)
|
| Appl. No.:
|
812517 |
| Filed:
|
December 20, 1991 |
| Current U.S. Class: |
546/321; 546/168 |
| Intern'l Class: |
C07D 213/803 |
| Field of Search: |
546/250,168,321
|
References Cited
U.S. Patent Documents
| 4460776 | Sep., 1992 | Wepplo | 546/250.
|
| 4723011 | Feb., 1988 | Doehner | 546/250.
|
| 4904816 | Feb., 1990 | Cevasco et al. | 560/44.
|
| 4997947 | Mar., 1991 | Szczepanski | 546/278.
|
| Foreign Patent Documents |
| 0292032 | Nov., 1988 | EP | 546/278.
|
| 0299362 | Jan., 1989 | EP | 546/278.
|
Other References
Konishi, Chemical Abstracts, 86:139407g May 5, 1977.
Sumi et al., Chemical Abstracts, 70:67660d Sep. 25, 1967.
|
Primary Examiner: Ivy; C. Warren
Assistant Examiner: Davis; Zinna N.
Attorney, Agent or Firm: Hogan, Jr.; John W.
Claims
I claim:
1. A process for the purification of a 2,3-pyridine or
quinolinedicarboxylic acid diester having the structural formula I
##STR6##
wherein X and Y are each independently hydrogen, halogen, C.sub.1 -C.sub.6
alkyl, C.sub.1 -C.sub.4 hydroxyalkyl, C.sub.1 -C.sub.4 alkoxyalkyl,
C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.4 alkylthio, phenoxy, C.sub.1
-C.sub.4 haloalkyl, nitro, cyano, C.sub.1 -C.sub.4 alkylamino,
diloweralkylamino, C.sub.1 -C.sub.4 alkylsulfonyl or phenyl optionally
substituted with a C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or
halogen group; and, when taken together, X and Y may form a ring in which
XY is represented by the structure
##STR7##
wherein L, M, Q and Z are each hydrogen, halogen, C.sub.1 -C.sub.4 alkyl
or C.sub.1 -C.sub.4 alkoxy; and
R and R.sub.1 are each independently
C.sub.1 -C.sub.6 alkyl optionally substituted with C.sub.1 -C.sub.4 alkoxy
or phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups or halogen atoms, or
phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups or halogen atoms;
which comprises washing a mixture of an impure formula I compound and a
first solvent with between about 0.2 to 1.2 molar equivalents of a 5% to
20%, by weight, mineral acid solution, extracting the washed organic
mixture with at least about 2.0 molar equivalents of a 40% to 85%, by
weight, mineral acid solution, diluting the concentration of the mineral
acid in the aqueous acid extract to a value of 5% to 30%, by weight, with
water and extracting the diluted aqueous acid extract with a second
solvent to obtain a purified formula I compound.
2. The process according to claim 1 wherein the washed organic mixture is
extracted with about 2.0 to 6.0 molar equivalents of a 45% to 65%, by
weight, mineral acid solution.
3. The process according to claim 1 wherein the mineral acid is selected
from the group consisting of sulfuric acid, hydrochloric acid, hydrobromic
acid and phosphoric acid and the first solvent and second solvent are
independently selected from the group consisting of toluene, benzene, a
xylene, chlorobenzene and a dichlorobenzene.
4. The process according to claim 3 wherein the mineral acid is sulfuric
acid and the first solvent and the second solvent are toluene.
5. The process according to claim 1 wherein X and Y are each independently
hydrogen, C.sub.1 -C.sub.6 alkyl or
C.sub.1 -C.sub.4 alkoxyalkyl; and, when taken together, X and Y may form a
ring in which XY is represented by the structure --CH.dbd.CH--CH.dbd.CH--;
and
R and R.sub.1 are each independently C.sub.1 -C.sub.6 alkyl.
6. The process according to claim 5 wherein the 2,3-pyridine or
quinolinedicarboxylic acid diester is selected from the group consisting
of diethyl 5-ethyl-2,3-pyridinedicarboxylate, diethyl
2,3-pyridinedicarboxylate, diethyl
5-methoxymethyl-2,3-pyridinedicarboxylate, diethyl
2,3-quinolinedicarboxylate and diethyl 5-methyl-2,3-pyridinedicarboxylate.
7. The process according to claim 6 wherein the 2,3-pyridine or
quinolinedicarboxylic acid diester is diethyl
S-ethyl-2,3-pyridinedicarboxylate.
8. A process for the purification of a 2,3-pyridine or
quinolinedicarboxylic acid diester having the structural formula I
##STR8##
wherein X and Y are each independently hydrogen, halogen, C.sub.1 -C.sub.6
alkyl, C.sub.1 -C.sub.4 hydroxyalkyl, C.sub.1 -C.sub.4 alkoxyalkyl,
C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.4 alkylthio, phenoxy, C.sub.1
-C.sub.4 haloalkyl, nitro, cyano, C.sub.1 -C.sub.4 alkylamino,
diloweralkylamino, C.sub.1 -C.sub.4 alkylsulfonyl or phenyl optionally
substituted with a C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or
halogen group; and, when taken together, X and Y may form a ring in which
XY is represented by the structure
##STR9##
wherein L, M, Q and z are each hydrogen, halogen, C.sub.1 -C.sub.4 alkyl
or C.sub.1 -C.sub.4 alkoxy and
R and R.sub.1 are each independently
C.sub.1 -C.sub.6 alkyl optionally substituted with C.sub.1 -C.sub.4 alkoxy
or phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups or halogen atoms, or
phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups or halogen atoms;
which comprises extracting an impure formula I compound, optionally in the
presence of a first solvent, with at least about 2.0 molar equivalents of
a 40% to 85%, by weight, mineral acid solution, diluting the concentration
of the mineral acid in the aqueous acid extract to a value of 5% to 30%,
by weight, with water and extracting the diluted aqueous acid extract with
a second solvent to obtain a purified formula I compound.
9. The process according to claim a wherein the impure formula I compound
is extracted with a mineral acid in the presence of a first solvent.
10. The process according to claim 8 wherein the mixture of an impure
formula I compound is extracted with about 2.0 to 6.0 molar equivalents of
a 45% to 65%, by weight, mineral acid solution.
11. The process according to claim a wherein the mineral acid is selected
from the group consisting of sulfuric acid, hydrochloric acid, hydrobromic
acid and phosphoric acid and the second solvent is selected from the group
consisting of toluene, benzene, a xylene, chlorobenzene and a
dichlorobenzene.
12. The process according to claim 11 wherein the mineral acid is sulfuric
acid and the first solvent is toluene.
13. The process according to claim 8 wherein the 2,3-pyridine or
quinolinedicarboxylic acid diester is selected from the group consisting
of diethyl 5-ethyl-2,3-pyridinedicarboxylate, diethyl
2,3-pyridinedicarboxylate, diethyl
5-methoxymethyl-2,3-pyridinedicarboxylate, diethyl
2,3-quinolinedicarboxylate and diethyl 5-methyl-2,3-pyridinedicarboxylate.
14. A process for the purification of a 2,3-pyridine or
quinolinedicarboxylic acid diester having the structural formula I
##STR10##
wherein X and Y are each independently hydrogen, halogen, C.sub.1 -C.sub.6
alkyl, C.sub.1 -C.sub.4 hydroxyalkyl, C.sub.1 -C.sub.4 alkoxyalkyl,
C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.4 alkylthio, phenoxy, C.sub.1
-C.sub.4 haloalkyl, nitro, cyano, C.sub.1 -C.sub.4 alkylamino,
diloweralkylamino, C.sub.1 -C.sub.4 alkylsulfonyl or phenyl optionally
substituted with a C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or
halogen group; and, when taken together, X and Y may form a ring in which
XY is represented by the structure
##STR11##
wherein L, M, Q and Z are each hydrogen, halogen, C.sub.1 -C.sub.4 alkyl
or C.sub.1 -C.sub.4 alkoxy and
R and R.sub.1 are each independently
C.sub.1 -C.sub.6 alkyl optionally substituted with C.sub.1 -C.sub.4 alkoxy
or phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups or halogen atoms, or
phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups or halogen atoms;
which comprises extracting an impure formula I compound, optionally in the
presence of a first solvent, with at least about 2.0 molar equivalents of
a 40% to 85%, by weight, mineral acid solution, neutralizing the aqueous
acid extract with base and extracting the neutralized aqueous extract with
a second solvent to obtain a purified formula I compound.
15. The process according to claim 14 wherein the impure formula I compound
is extracted with a mineral acid solution in the presence of a solvent.
16. The process according to claim 14 wherein the impure formula I compound
is extracted with about 2.0 to 6.0 molar equivalents of the mineral acid
solution.
17. The process according to claim 16 wherein the mineral acid is selected
from the group consisting of sulfuric acid, hydrochloric acid, hydrobromic
acid and phosphoric acid, the first solvent and the second solvent are
independently selected from the group consisting of toluene, benzene, a
xylene, chlorobenzene and a dichlorobenzene and the base is selected from
the group consisting of ammonium hydroxide, sodium carbonate and sodium
bicarbonate.
18. The process according to claim 17 wherein the mineral acid is sulfuric
acid, the first and second solvents are toluene and the base is ammonium
hydroxide.
19. The process according to claim IS wherein the 2,3-pyridine or
quinolinedicarboxylic acid diester is selected from the group consisting
of diethyl 5-ethyl-2,3-pyridinedicarboxylate, diethyl
2,3-pyridinedicarboxylate, diethyl
5-methoxymethyl-2,3-pyridinedicarboxylate, diethyl
2,3-quinolinedicarboxylate and diethyl 5-methyl-2,3-pyridinedicarboxylate.
20. The process according to claim 19 wherein the 2,3-pyridine or
quinolinedicarboxylic acid diester is diethyl
5-ethyl-2,3-pyridinedicarboxylate.
Description
BACKGROUND OF THE INVENTION
The discovery, development and commercialization of the
2-(2-imidazolin-2-yl)pyridine and quinoline compounds as herbicidal agents
has given new meaning to the term "weed control"; for within this series
of compounds it has been found that some are broad-spectrum or total
vegetation herbicides with activity in both herbaceous and woody plants.
Others are highly selective weed control agents useful as weed control
agents in the presence of crops.
Several processes for the preparation of the herbicidal
2-(2-imidazolin-2-yl)pyridines involve the preparation of
2,3-pyridinedicarboxylic acids from 2,3-pyridinedicarboxylic acid
diesters, but methods for the preparation of 2,3-pyridinedicarboxylic acid
diesters produce impure products. Current methods of production of
2.3-pyridinedicarboxylic acid diesters by various condensation routes
provide very impure products (20% to 50% purity). Arduous or
time-consuming purification methods are required to provide purified
2.3-pyridinedicarboxylic acid diesters. Distillation has been used to
improve the purity initially to as high as about 65% to 70%. However, the
distillation is done at high temperatures and at high vacuum and the
distillation product is further purified by a second distillation to
obtain purified 2,3-pyridinedicarboxylic acid diesters.
Since the purity of the 2,3-pyridinedicarboxylic acid diesters impact
directly on the purity of the 2,3-pyridinedicarboxylic acids, a process
that would improve the purity of the 2.3-pyridinedicarboxylic acid
diesters without requiring the use of time-consuming distillation
procedures would provide a great improvement in the processes used to
prepare the herbicidal 2-(2-imidazolin-2-yl)pyridine and quinoline
compounds.
It is an object of the present invention to provide a process for the
purification of 2,3-pyridine and quinolinedicarboxylic acid diester
compounds which avoids the use of the arduous or time-consuming
purification methods of the prior art.
SUMMARY OF THE INVENTION
The present invention relates to an efficient process for the purification
of 2,3-pyridine and quinolinedicarboxylic acid diesters of formula I
##STR1##
wherein X and Y are each independently hydrogen, halogen, C.sub.1 -C.sub.6
alkyl, C.sub.1 -C.sub.4 hydroxyalkyl, C.sub.1 -C.sub.4 alkoxyalkyl,
C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.4 alkylthio, phenoxy, C.sub.1
-C.sub.4 haloalkyl, nitro, cyano, C.sub.1 -C.sub.4 alkylamino,
di-loweralkylamino C.sub.1 -C.sub.4 alkylfulfonyl or phenyl optionally
substituted with a C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or
halogen group; and, when taken together, X and Y may form a ring in which
XY is represented by the structure
##STR2##
wherein L, M, Q and Z are each hydrogen, halogen, C.sub.1 -C.sub.4 alkyl
or C.sub.1 -C.sub.4 alkoxy; and
R and R.sub.1 are each independently
C.sub.1 -C.sub.6 alkyl optionally substituted with C.sub.1 -C.sub.4 alkoxy
or phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups or halogen atoms, or
phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups, or halogen atoms;
which comprises extracting an impure mixture containing the said formula I
compound, optionally in the presence of a solvent, with at least about 2.0
molar equivalents of a 40% to 85%. by weight, mineral acid solution. The
aqueous acid extract is neutralized with base to provide purified formula
I compounds directly or by extracting the neutralized mixture with a
solvent. Alternatively, the aqueous acid extract is diluted with water and
extracted with a solvent to provide purified formula I compounds.
Advantageously, the process of the invention avoids the use of
time-consuming distillation purification procedures. Furthermore, the
mineral acid present in the aqueous acid solution, after extraction with a
solvent, is readily recycled into the process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In one of the preferred embodiments of the invention, the formula I
pyridine and quinolinedicarboxylic acid diester compounds are purified by
washing a mixture of an impure formula I compound and a solvent with
between about 0.2 to 1.2 molar equivalents of a 5% to 20%, by weight,
mineral acid solution, extracting the washed organic mixture with at least
about 2.0 molar equivalents, preferably about 2.0 to 6.0 molar
equivalents, of a 40% to 85%, by weight, mineral acid solution, diluting
the concentration of the mineral acid in the aqueous acid extract to a
value of about 5% to 30%, by weight, with water and extracting the diluted
aqueous acid extract with a solvent to obtain purified formula I
compounds.
Advantageously, the dilute acid wash removes acid soluble impurities from
the impure formula I compound. Since the acid soluble impurities are
removed, a purer formula I compound is obtained from the aqueous mineral
acid extraction.
Another embodiment of the invention comprises extracting an impure formula
I compound, optionally in the presence of a solvent, with at least about
2.0 molar equivalents, preferably about 2.0 to 6.0 molar equivalents, of a
40% to 85%, by weight, mineral acid solution, diluting the concentration
of the mineral acid in the aqueous acid extract to a value of 5% to 30%,
by weight, with water and extracting the diluted aqueous acid extract with
a solvent to obtain purified formula I compounds.
A further embodiment of the invention comprises extracting an impure
formula I compound, optionally in the presence of a solvent, with at least
about 2.0 molar equivalents, preferably about 2.0 to 6.0 molar
equivalents, of a 40% to 85%, by weight, mineral acid solution,
neutralizing the aqueous acid extract with base and extracting the
neutralized aqueous extract with a solvent to obtain purified formula I
compounds.
In the above embodiments of the invention, the purified formula I compounds
may be isolated by evaporating the resultant extract, or the extract
containing the purified formula I compound may be sent directly to the
reaction used to obtain the corresponding pyridine or
quinolinedicarboxylic acid compound.
mineral acids which are suitable for use in the present invention include
sulfuric acid, hydrochloric acid, hydrobromic acid, phosphoric acid and
the like with sulfuric acid being preferred. A 45% to 65%, by weight,
mineral acid solution is preferred. Solvents which are useful in the
present invention include aromatic hydrocarbons such as toluene, benzene
and xylenes, halogenated aromatic hydrocarbons such as chlorobenzene and
dichlorobanzenes, and the like. Toluene and chlorobenzone are preferred
solvents. Bases suitable for use in the process of the invention include
ammonium hydroxide, sodium carbonate, sodium bicarbonate and the like with
Ammonium hydroxide being preferred.
The above processes are especially efficacious for the purification of
formula I compounds wherein
X and Y are each independently hydrogen, C.sub.1 -C.sub.6 alkyl or C.sub.1
-C.sub.4 alkoxyalkyl; and, when taken together, X and Y may form a ring in
which XY is represented by the structure --CH.dbd.CH--CH.dbd.CH--; and
R and R.sub.1 are each independently C.sub.1 -C.sub.6 alkyl.
Preferred formula I compounds that are purified by the processes of the
invention are diethyl 5-ethyl-2,3-pyridinedicarboxylate, diethyl
2,3-pyridinedicarboxylate, diethyl
5-methoxymethyl-2,3-pyridinedicarboxylate, diethyl
2,3-quinolinedicarboxylate and diethyl 5-methyl-2,3-pyridinedicarboxylate.
The processes of the invention provide purified formula I compounds without
requiring the use of arduous or time consuming distillations done at high
temperatures and high vacuum.
Formula I compounds are described in U.S. Pat. No. 4,723,011; U.S. Pat. No.
4,997,947; European application 292-0931-A published Nov. 23, 1988 and
European application 299-362-A published Jan. 18, 1989.
The purified formula I compounds are useful as starting materials for the
preparation of herbicidal 2-(2-imidazolin-2-yl)pyridine and quinoline
compounds having the structural formula II
##STR3##
wherein R.sub.2 is C.sub.1 -C.sub.4 alkyl
R.sub.3 is C.sub.1 -C.sub.4 alkyl or C.sub.3 -c.sub.6 cycloalkyl; and when
R.sub.2 and R.sub.3 are taken together with the carbon to which they are
attached they may represent C.sub.3 -C.sub.6 cycloalkyl optionally
substituted with methyl; and
X and Y are each independently hydrogen, halogen, C.sub.1 -C.sub.6 alkyl,
C.sub.1 -C.sub.4 hydroxyalkyl, C.sub.1 -C.sub.4 alkoxyalkyl, C.sub.1
-C.sub.6 alkoxy, C.sub.1 -C.sub.4 alkylthio, phenoxy, C.sub.1 -C.sub.4
haloalkyl, nitro, cyano, C.sub.1 -C.sub.4 alkylamino, diloweralkylamino,
C.sub.1 -C.sub.4 alkylsulfonyl or phenyl optionally substituted with a
C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or halogen group; and,
when taken together, X and Y may form a ring in which XY is represented by
the structure
##STR4##
wherein L, M, Q and Z are each hydrogen, halogen, C.sub.1 -C.sub.4 alkyl
or C.sub.1 -C.sub.4 alkoxy; and
R and R.sub.1 are each independently C.sub.1 -C.sub.6 alkyl optionally
substituted with C.sub.1 -C.sub.4 alkoxy or phenyl optionally substituted
with one to three C.sub.1 -C.sub.4 alkyl groups, C.sub.1 -C.sub.4 alkoxy
groups or halogen atoms, or
phenyl optionally substituted with one to three C.sub.1 -C.sub.4 alkyl
groups, C.sub.1 -C.sub.4 alkoxy groups, or halogen atoms.
A method used to manufacture formula II 2-(2-imidazolin-2-yl)pyridine and
quinoline herbicidal agents from formula I pyridine and
quinolinedicarboxylic acid diesters is shown below in Flow Diagram I.
##STR5##
In order to facilitate a further understanding of the invention, the
following examples are presented to illustrate more specific details
thereof. The invention is not to be limited thereby except as defined in
the claims. The term HPLC designates high pressure liquid chromatography.
EXAMPLE 1
Purification of Diethyl 5-ethyl-2,3-pyridinedicarboxylate with an initial
dilute acid wash
A 15%, by weight, sulfuric acid solution (0.200 mol) is added with stirring
to a solution of diethyl 5-ethyl-2,3-pyridinedicarboxylate (100.00 g,
50.3% real, 0.200 mol) in toluene (400 mi). The organic layer is separated
and extracted with 60%, by weight, sulfuric acid solution (0.651 mol). The
aqueous extract is diluted with ice-water (316.50 g) and extracted with
toluene (200 mi). The organic extract (228.4 g) is concentrated in vacuo
to give purified diethyl S-ethyl-2,3-pyridinedicarboxylate (55.26 g, 77.2%
real, isolated yield 84.8%).
This example shows that when the impure diethyl
5-ethyl-2,3-pyridinedicarboxylate mixture is first washed with dilute
sulfuric acid, to remove acid soluble impurities, followed by extraction
with a strong sulfuric acid solution, that the purity of the said
dicarboxylate is increased by 53.5% with an isolated yield of 84.8%.
EXAMPLES 2-10
Purification of Diethyl 5-ethyl-2,3-pyridinedicarboxylate by extraction
with sulfuric acid
A solution of diethyl 5-ethyl-2,3-pyridinedicarboxylate (34.46 g, 72.6%
real, 0.10 mol) in toluene (65.54 g) is extracted with a 32.36%, by
weight, sulfuric acid solution (0.2 mol). The organic phase is washed with
10% sodium bicarbonate solution and water. The combined water and sodium
bicarbonate washes are washed with toluene and the toluene wash is
combined with the organic phase. The organic phase is concentrated in
vacuo to a constant weight and the unextracted diethyl
5-ethyl-2,3-pyridinedicarboxylate is then assayed by HPLC. The results of
this example are summarized in Table I below.
Following the above procedure, but varying the sulfuric acid concentrations
and number of equivalents utilized, gives the results summarize4 in Table
I below.
TABLE I
__________________________________________________________________________
Purification of Diethyl 5-ethyl-2,3-pyridinedicarboxylate
Example Number
2 3 4 5 6 7 8 9 10
__________________________________________________________________________
H.sub.2 SO.sub.4 concentration
32.36
43.06
64.35
48.40
59.45
77.05
57.98
68.10
82.48
(% w/w)
H.sub.2 SO.sub.4 equivalents
2 2 2 4 4 4 6 6 6
Weight of unextracted
20.3
13.13
3.41
2.85
0.52
0.20
0.21
0.33
0.37
diethyl 5-ethyl-2,3-
pyridinedicarboxylate
(g)
Purity of unextracted
73.6
65.9
37.5
34.6
10.5
5.1
4.8
8.3
3.6
diethyl 5-ethyl-2,3-
pyridinedicarboxylate
(% w/w)
Calculated weight of
4.68
11.88
21.59
22.15
24.48
24.80
24.79
24.68
24.64
extracted diethyl 5-
ethyl-2,3-pyridine-
dicarboxylate (g)
Calculated purity
68.3
81.6
85.1
84.5
82.9
81.2
82.4
80.7
77.5
of extracted diethyl
5-ethyl-2,3-pyridine-
dicarboxylate
(% w/w)
Calculated extracted
18.72
47.52
86.36
88.60
97.92
99.20
99.16
98.72
98.56
recovery of 5-ethyl-
2,3-pyridinedicar-
boxylate (%)
__________________________________________________________________________
As can be seen from the data in Table I above, the purity of the diethyl
S-ethyl-2,3-pyridinedicarboxylate is generally improved to greater than
81% (up from 72.6%) using 2-6 equivalents of sulfuric acid solutions
having concentrations greater than 43%. Although upon first inspection the
increase in purity from 72.6% to generally greater than 81% may not appear
to be a significant increase, it results in a dramatic improvement when
commercially manufacturing the 2-(2-imidazolin-2-yl)pyridine and quinoline
herbicides. Note that by employing the preferred 45%-65%, by weight,
mineral acid solutions the purity of the diethyl 5-ethyl-2,3-pyridine
dicarboxylate is improved to 82% to 85%.
EXAMPLE 11
Purification of neat Diethyl 5-ethyl-2,3-pyridinedicarboxylate by
extraction with sulfuric acid
Diethyl 5-ethyl-2,3-pyridinedicarboxylate (29.0 g, 70.2% real, 0.081 mol)
is added to a stirred mixture of water (50 mi) and 96% sulfuric acid
(30.37 g). The mixture is allowed to settle and the phases are separated.
The aqueous layer, which contains a small amount of an oil, is stirred
with diatomaceous earth (2.0 g), filtered and washed with water (10 mi).
The combined filtrate and wash is neutralized with 30% Ammonium hydroxide
solution (36.22 g) and extracted with toluene. The combined organic
extracts are concentrated in vacuo to obtain a brown oil and a small
amount of a solid. The oil is decanted from the solid to give purified
diethyl 5-ethyl-2,3-pyridinedicarboxylate (19.78 g, 81.5% real, 79.2% real
recovery).
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